Valve co-founder Gabe Newell announced during a DICE keynote today that last weekend's half-price sale of Left 4 Dead resulted in a 3000% increase in sales of the game, posting overall sales that beat the title's original launch performance.

Newell also mentioned that new Steam customers jumped 1600% over the same weekend, according to G4TV. Retail sales remained constant.

Sales of Team Fortress 2 went up 106% following a free update to the game. Retail wasn't left out in this case, with sales jumping 28%.

The massive Steam holiday sale was also a big win for Valve and its partners. The following holiday sales data was released, showing the sales breakdown organized by price reduction:

10% sale = 35% increase in sales (real dollars, not units shipped)

25% sale = 245% increase in sales

50% sale = 320% increase in sales

75% sale = 1470% increase in sales

Furthermore, Valve has hired an experimental psychologist to maximize the excitement of Steam sales and other marketing opportunities. According to Newell, one suggestion by the psychologist was to provide one free copy of a Valve game to every 25th buyer of Left 4 Dead.